Plug-in hybrids are coming. General Motors, Tesla Motors, Fisker Automotive and Toyota are all coming out with gas-electric cars that can be charged from a socket.

The question now is can the grid handle it. The latest voice on the debate, Stan Hadley of the Cooling, Heating and Power Technologies Program at Oak Ridge National Laboratories, says it won't be easy. Hadley examined 182 scenarios on how plug-ins might be used in different regions in the U.S. between 2020 and 2030. Hadley assumed a 25 percent penetration of plug-ins by 2020.

In a worst case scenario, Hadley postulated that the U.S. would need 160 new power plants to handle the requirements of these cars. The worst case scenario, though, assumes that the millions of plug-in owners would want to charge their car at 5 p.m., the tail end of peak power demand.

In a best case scenario, where drivers charged their cars after 10 p.m. and smart grid technologies staggered charging times, the U.S. would need zero to eight new power plants.

Zero to 160 is a big swing, but Hadley warns that you have to accommodate human nature. Electricity costs less at night, so individuals will be incented to charge their cars then. But you also can't control everyone's behavior.

"It might prove extremely difficult to force consumers to charge their cars during some specified period of time," he wrote in his report. Continued, repeated charging could also stress the infrastructure of the grid, he added.

Overall, Hadley concluded that nearly every region in the country would have to beef up its electrical capacity. Electricity prices would also rise, by 1.2 to 2.7 percent in the best case scenarios to 141 to 297 percent in the worst case scenarios. The price hikes also depend on the size of the batteries used in the cars.

In Hadley's analysis, plug-ins could end up producing more carbon dioxide than efficient standard hybrids. But a plug-in hybrid is always better than driving a regular car.

"The best thing about plug-in hybrids is that they open us up to non-oil," he said in a phone conference. "But there are questions. Hybrids do a pretty good job themselves."
Hadley isn't alone in his skepticism of plug-ins. "Plug-in hybrids are irrelevant because they are too expensive. Unless you can make 500 million or 800 million of those, it won't matter," said noted VC Vinod Khosla recently. Plug-ins and electric cars, though, have a lot more adherents right now than detractors. It will take more information and studies to figure out who is right on this one.

Last year, the Pacific Northwest National Labs said that you could convert 73 percent of the cars, trucks and vans on the road in the U.S. to plug-ins and the grid, as it currently exists, could handle it. PNNL scientists, however, said that their study depended on night time charging and that it still needed to study the impact on the grid of sustained charging.